Different types and kinds of electro-acoustic transducers include loudspeakers or microphones, for example. Each one includes a movable diaphragm, which interacts with the surrounding atmosphere either to produce sound waves, or to be set into motion by sound waves. As will becomes apparent to those skilled in the art, the invention relates to either of these types of electro-acoustic transducers. However, for clarity, only loudspeakers will be shown and described herein.
Conventional conically-shaped loudspeakers, by the very shape of the cone, produce distortion in the sound emitted thereby. Such distortion is known as the "cavity effect". Sound propagating from the speaker cone is not emitted uniformly from the surface thereof, because sound waves emitted from the central portion of the cone may be out of phase with the sound emitted from the peripheral portions thereof. As a generality, the latter sound waves travel a shorter distance from the diaphragm to the listener, as compared to the waves emitted from the central portion of the cone.
The specification in the above-identified parent applications identifies a number of prior patents which deal with this problem in different ways. The parent application then described another way of attacking the problem by providing a flat diaphragm with projections on one side for carrying a voice coil into a plurality of spaced parallel gaps in a magnetic structure. This flat diaphragm and magnetic structure greatly reduces, if not completely minimizes, speaker distortion, and yet is highly efficient in operation. Also, the flat piston acts as a true piston, as distinguished from a cone, for example, which may send out arcuate wave fronts. In this regard, the inventive diaphragm is lightweight, and yet has the capability of including an adequate number of voice coil conductors, to obtain satisfactory impedance characteristics. That diaphragm is substantially rigid, to maintain a proper alignment of its conductors within the gaps of its magnetic structure, during operation. Also, the flat diaphragm of the parent application is relatively less expensive to manufacture as compared to other prior art diaphragms.
A further effort has produced a flat diaphragm for use in the structure of the parent invention which is significantly better than other flat diaphragms that may also be used in such structure. In particular, it was found that the aerodynamic design of the flat diaphragm could be improved by providing a better mechanical balance. Ideally, the diaphragm should have a center of gravity at the geometrical center of the diaphragm.
Conceptually, if the diaphragm is cut along any of the infinite number of lines that pass through the center of gravity in the plane of the diaphragm, and if each of the two resulting halves is weighed, each half has precisely the same weight that the other half has. It may not be possible to always provide the ideal weight distribution since nothing is ever that perfect; however, it has been found that the ideal weight may be closely approached by the relatively simple procedure of selecting a particular geometrical pattern of voice coil conductors.